The short answer
For wildfire smoke, the EPA says to use a filter rated at least MERV 13, or as high as your HVAC fan and filter slot can handle. During a smoke event in Vancouver WA, also set the thermostat fan to "on" instead of "auto," switch any fresh-air intake to recirculate, and replace the filter about every 30 days. Portable air cleaners cover bedrooms; a whole-home air cleaner adds another layer.
In this guide
Smoke smell is a different fix. The steps below remove smoke particles, which is what the AQI number measures. Smoke odor is a gas, and it passes straight through even a MERV 13 filter. If your house smells like a campfire, read how to get wildfire smoke smell out of your house.
Step 1: Upgrade your filter to MERV 13.
For wildfire smoke, the EPA says to choose a filter rated at least MERV 13, or as high a rating as your system fan and filter slot can handle, because fine particles are the biggest health threat in smoke. In the EPA's MERV table, a MERV 13 filter captures at least 50% of particles 0.3 to 1.0 microns and at least 85% of particles 1.0 to 3.0 microns.
MERV (Minimum Efficiency Reporting Value) is a 1–16 scale rating how well a filter captures particles from 0.3 to 10 microns. A MERV 8, a common 1-inch furnace filter, is rated in the EPA's table only for particles 1 micron and larger.
The EPA notes that you may need an HVAC technician to tell you the highest-rated filter your system can take. A few considerations:
- Airflow restriction. Higher-MERV filters are denser. If your system has marginal airflow already, jumping to MERV 13 in a 1-inch filter slot can starve the air handler. The fix is usually a 4-inch or 5-inch media cabinet, which has the surface area to run MERV 13 with less pressure drop.
- Sizing. Buy the exact size, filter dimensions are listed on the side of the existing filter. The EPA says the filter should fit snugly so air does not leak around it; an off-by-half-an-inch filter leaves a gap that smoky air slips through.
- Read the label. Look for MERV 13 printed on the filter itself. Some brands rate filters on their own scales instead, such as 3M's MPR or Home Depot's FPR. For AprilAire media cabinets, the MERV 13 filter number depends on the cabinet model (the 213, 313 and 413 are all MERV 13), so match it to the model on your cabinet.
Step 2: Switch to recirculate mode.
Recirculate mode stops pulling outdoor smoke into the house and keeps cycling the existing indoor air through your filter. If your system has a fresh-air intake (some newer homes with HRV/ERV systems do), the EPA says to set it to recirculate or close the outdoor intake damper during smoke events.
On a standard thermostat, also set the fan to "on" instead of "auto," as the EPA advises when a high-efficiency filter is installed. That keeps air moving through the filter continuously, even when the system is not actively heating or cooling.
Step 3: Replace the filter more often.
During heavy smoke, the EPA says to plan on replacing the filter more often than the manufacturer recommends, and to change it when it looks dirty. We suggest about every 30 days. You can usually see it, the filter media goes from white to gray to dark gray. When airflow at supply registers feels noticeably weaker, replace it immediately.
We recommend keeping at least two spare MERV 13 filters in the closet during August and September. Cheap insurance.
Step 4: Add an air purifier.
A whole-home air purifier that integrates with the HVAC system adds another layer, especially for anyone with asthma, COPD, young children, or elderly residents. We install them and price one as an optional line item on your quote.
For bedrooms and the room where you spend the most time, the EPA recommends a portable air cleaner sized for the room that does not produce ozone. We recommend one per bedroom for households with anyone in a sensitive group.
What does not help (and may hurt).
- Opening windows "for fresh air." Counterproductive during a smoke event. The outdoor air is the problem.
- Opening up before the air actually clears. The EPA says to air the house out when outdoor air quality improves, even temporarily. Check the current reading on AirNow first, open up while it stays low, and close up again when it climbs.
- "Air cleaning" sprays or candles. Marketing. Some actively make air quality worse by adding VOCs.
- Running an attic fan or whole-house fan. These pull outdoor air directly into the home. Disable them entirely during smoke events.
Tracking when to act
The Washington Department of Ecology and Oregon DEQ both publish hourly AQI for Vancouver and Portland. The PurpleAir map (purpleair.com) is more granular: sensors on individual streets show wide variation across the metro, so we watch it more than the official AQI during smoke events.
What we install for clients who want a full solution.
Our full smoke-season setup has four parts:
- 4-inch media cabinet retrofit on the air handler return (replaces the 1-inch filter slot)
- AprilAire MERV 13 media filter sized to the cabinet (AprilAire recommends replacing it every 12 months, sooner during smoke season)
- Smart thermostat with fan scheduling, set to circulate 20 minutes per hour by default, ramp to continuous during AQI events
- Optional: a whole-home air cleaner for an extra capture stage
We price the media cabinet and any air cleaner as optional line items. For help setting either one up, request a quote. We typically schedule these in May or June, before smoke season starts.
Questions homeowners ask.
What's the single most important step to protect indoor air during a wildfire smoke event?
Upgrading your filter to MERV 13. MERV (Minimum Efficiency Reporting Value) is a 1-16 scale rating how well a filter captures particles from 0.3 to 10 microns. For wildfire smoke, the EPA says to use a filter rated at least MERV 13, or as high as your system fan and filter slot can handle, because fine particles are the biggest health threat in smoke. In the EPA's MERV table, a MERV 13 filter captures at least 50% of particles 0.3 to 1.0 microns and at least 85% of particles 1.0 to 3.0 microns, while a MERV 8 has no rating at all for the 0.3 to 1.0 micron range. A system with marginal airflow may need a 4-inch or 5-inch media cabinet to run one.
What is recirculate mode, and how do you set it up on a standard thermostat?
Recirculate mode stops pulling outdoor smoke into the house and keeps cycling the existing indoor air through your filter instead. If your system has a fresh-air intake (some newer homes with HRV/ERV systems do), the EPA says to set it to recirculate or close the outdoor intake damper during smoke events. On a standard thermostat, also set the fan to 'on' instead of 'auto,' which keeps air moving through the filter continuously even when the system isn't actively heating or cooling. The extra fan runtime is worth it during smoke season.
How often should you replace your filter during a heavy smoke event?
During heavy smoke, the EPA says to plan on replacing an HVAC filter more often than the manufacturer recommends and to change it when it looks dirty; we suggest about every 30 days. You can usually see it happening, the filter media goes from white to gray to dark gray, and when airflow at supply registers feels noticeably weaker, it's time to replace it immediately. It's worth keeping at least two spare MERV 13 filters in the closet during August and September, cheap insurance against getting caught without one mid-smoke-season.
What whole-home upgrades does Pacific Peak install for wildfire smoke?
Pacific Peak installs 4-inch or 5-inch media filter cabinets on the return, which hold a thicker MERV 13 filter with more surface area than a 1-inch slot, and can add a whole-home air cleaner to the HVAC system; both are priced as optional line items on your quote. For bedrooms and the room where you spend the most time, the EPA recommends a portable air cleaner sized for the room that does not produce ozone.
What HVAC habits actually hurt indoor air quality during a wildfire smoke event?
Several common habits backfire. Opening windows 'for fresh air' is counterproductive since the outdoor air is the problem. Opening up before the outdoor air actually improves is another; the EPA says to air the house out only when outdoor air quality improves, even temporarily, so check the current reading first. 'Air cleaning' sprays or candles are mostly marketing and some actively add VOCs that worsen air quality. And running an attic fan or whole-house fan pulls outdoor air directly into the home, so these should be disabled entirely during smoke events.
Sources and resources
Reviewed for accuracy by Sam Tsarenko, founder of Pacific Peak Mechanical. This guide draws on the following primary sources:
Related from Pacific Peak: How to get smoke smell out of your house · HVAC repair in Vancouver WA · How often to change your furnace filter
